As shown in FIG. 36, there has been a conventional light emitting device formed by a process in which one LED chip (or several LED chips) 710 are mounted on a package substrate 700 mounted with lead frames 701, in which an n-type electrode 705 and a p-type electrode 706 of the LED chip 710 are connected to the lead frames 701 by bonding wires 711 and 712, respectively, in which resin 722 containing fluorescent substances is thereafter applied on the LED chip 710 surrounded with reflector plates 721, and in which transparent resin 723 is applied on the resin 722 containing the fluorescent substances (see Non-Patent Literature 1, for instance). In the LED chip 710, a semiconductor layer 703 made of GaN is stacked on a sapphire substrate 702, and an active layer 704 is included in the semiconductor layer 703.
Hereinbelow, a method of heat radiation from the LED that is a conventional light emitting device will be described with use of FIG. 37 that is schematized. A common LED chip is in shape of a square with each side 500 μm long and has a thickness of 10 μm, for instance (light emitting area of 250,000 μm2 (=500 μm×500 μm)). The size of the LED chip is sufficiently larger than thickness (e.g., 100 μm) of a thermally conductive substrate 801 that serves to efficiently dissipate heat from the LED. In this configuration, as shown in a schematic section of FIG. 37, heat produced by light emission flows out in a generally perpendicular direction toward the resin substrate 800 in parts except periphery of the LED chip 802. A metal film, a metal film with which an insulator film is coated, or the like is used as the thermally conductive substrate 801.
On the periphery of this LED chip 802, heat outflow in lateral directions in the thermally conductive substrate 801 is allowed, and thus quantity of heat outflow is increased. There is a problem in that resultant higher temperatures in center area than in the periphery in the active layer region (light emitting layer region) of the LED chip 802 lead to increase in temperatures of the active layer and consequent decrease in efficiency of light emission or lead to deterioration of transparent resin, fluorescent substances and/or the like that are adjacent thereto and decrease in life thereof.
The light emitting devices each having one LED chip (or several LED chips) installed therein have another problem of poor yield of the light emitting devices because variation in brightness, or luminance of the LED chips becomes variation in luminance of the light emitting devices as it is.
The light emitting devices have another problem in that concentration of luminous flux on an LED chip 901 mounted on a substrate 900, as shown in a schematic section of FIG. 39, results in deterioration of resin 902 covering the LED chip 901, which may cause decrease in efficiency of light emission therefrom and in life thereof (a thermally conductive substrate is omitted in FIG. 39).
Non-Patent Literature 1: Gen Murakami “No. 13 Transition of Semiconductor Packaging Technology for LEDs and LDs”, Semiconductor FPD World, PRESS JOURNAL INC., May 2009, pp. 114-117 (FIG. 5)